Mitsubishi Electric PUHY-HP120TNU-A, Service Handbook

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[5-2 Outdoor Unit Control ]
HWE18240_GB chapter 5 -
13
5 Control
5-2-7 Defrost Operation Control
(1) Starting the defrost operation
Œ
The defrost cycle will start when all of the three conditions (outside temperature, cumulative compressor operation time, and
pipe temperature) under <Condition 1>, <Condition 2>, or <Condition 3> are met.
1) Evaporating temperature (Te)
Œ
The defrost cycle will not start if other outdoor units are in the defrost cycle or until a minimum of 10 minutes have passed
since the completion of the last defrost cycle.
Œ
If 10 minutes have passed since compressor startup or since the completion of a defrost cycle, a forced defrost cycle can be
started by setting DIP SW4(913) to ON.
Œ
Even if the defrost-prohibit timer is set to 90 minutes, the actual defrost-prohibit time for the next defrost cycle is 50 minutes
if the last defrost cycle took 12 minutes.
Œ
All units in the heating mode will simultaneously go into the defrost cycle in a system with multiple units. The units that are
not in operation may or may not go into the defrost cycle, depending on the cumulative operation time of their compressors.
Condition 1 Condition 2 Condition 3
Outside temperature
(TH7) -5ºC [23ºF] or above -5ºC [23ºF] or below
Cumulative compressor
operation time 50 minutes or more
90 minutes or more if the defrost prohibit timer is set to 90.
250 minutes or more
Evaporating tempera-
ture (Te) The evaporating temperature
has stayed below the tempera-
ture in the table below (Note1)
for 3 minutes (Te
”
1.1 × TH7 - 7.5) continued
for 3 minutes or [{1.5 + 0.02 x
(20+TH7)} > 63LS] continued
for 3 minutes
The evaporating temperature
has stayed below the tempera-
ture in the table below (Note1)
for 3 minutes
HP72 - 120
SW4 (915) OFF -11 ºC
SW4 (915) ON -8 ºC